WO2003083981A1 - Proton exchanger for fuel cell and fuel cell containing the same - Google Patents

Abstract

A proton exchanger for fuel cell and a fuel cell. The fuel cell comprises a proton exchanger containing a basic compound having at least one heteroatom. In the fuel cell, an ionic liquid as a constituent of the proton exchanger is of low melting point and, without dependence on water, exhibits high conductivity.

Description

 Specification

 Proton exchanger for fuel cell and fuel cell provided with the same

 Technical field

 The present invention relates to a proton exchanger for a fuel cell using a novel proton-conductive substance, and more particularly, to a proton exchanger in which a composite is formed with a base material such as a polymer compound, and the like. And a fuel cell using the same.

 Background technology

 + Fuel cells using proton exchangers used as proton exchange membranes, etc. are attracting attention as power sources that achieve zero emission, and polymer solid oxide fuel cells (PEFC) are being developed for automobiles or as distributed power sources. Is becoming active. PEFC is basically composed of anode (electrode electrode), power electrode (air electrode), and polymer electrolyte membrane.By supplying hydrogen to the anode as fuel and oxygen to the power source, power is generated by the following reaction. Is performed.

Anode H ₂ → 2H + + 2e

Force Sword 2H + + 1/20 ₂ + 2e ~ → H ₂₀

 In order to carry out the above-mentioned battery reaction in PEFC, the anode must include a gas diffusion layer for uniformly supplying fuel hydrogen to the catalyst layer, an anode catalyst for extracting electrons from hydrogen, and collecting and transporting the electrons to an external circuit. It consists of a bipolar plate with an anode pole. Protons dissociated on the anode catalyst are transported by the electrolyte through the proton exchange membrane to the force sword.

 The power sword consists of a power sword catalyst that reacts protons and oxygen to generate water, a gas diffusion layer to uniformly supply oxygen to the catalyst layer, and a power sword bipolar plate that transports electrons to the cathode catalyst. You.

 In order to commercialize or commercialize PEFC, in addition to reducing the cost of catalysts, proton exchange membranes, bipolar plates, etc., the operating temperature must be higher, the moisture management must be simplified, and the startup characteristics at low temperatures must be improved. As a system, however, there are many issues to be solved due to the physical properties of the proton exchange membrane.

At present, proton exchange membranes of perfluorosulfonate polymer (commercially available under the trade names such as "Naphion" and "Flemion") are used as proton exchange membranes. However, these membranes cannot be operated at high temperatures due to (1) low heat resistance and (2) low temperature. (2) At an operating temperature of 80 ° C or higher, water is evaporated due to the dependence of proton conductivity on the presence of water. At a low temperature below 0, the proton conductivity is greatly reduced, and water in the membrane freezes, which greatly restricts the operation of the system. Therefore, in order to solve these problems, the development of a new proton exchange membrane technology and a system using the same is required as a breakthrough technology.

 Many membranes have been developed to solve such problems. For example, fluorine-free polymers such as polystyrene, polybenzoimidazole, and polyparaphenylene are being developed as hydrocarbon-based proton exchange membranes with the aim of improving heat resistance. However, these polymers solve the problem of proton exchange membranes composed of perfluorosulfonate-based high molecules, because at high temperatures of 10 oC or higher, ionic conductivity decreases due to water evaporation. I can't do that.

 On the other hand, since phosphoric acid dissociates protons even in the absence of water, anhydrous proton conductors using it are being studied. However, when phosphoric acid is used, the dissociation temperature of the proton is high, and as with the phosphoric acid fuel cell (PAFC), there are still problems such as corrosiveness, which has not been solved. .

 In addition, a new proton exchange membrane using a phenolic proton dissociating group is being studied, but it has not been possible to obtain a high proton conductivity.

iO傻合体力 プロトン 伝導性を示すことが 1976年に報告されている (T. Takahashi ら、 Solid State Chem.、 17卷、 353項、 1976年)。 Further, instead of conventional proton dissociating polymers, the aqueous solvent can be replaced by a solvate polymer containing no hydroxyl groups (eg, polyethylene oxide, polyvinylinolepyrrolidone, polyethyleneimine, or polyaminopropyl siloxane). As a result, an anhydrous proton conductor is obtained. For example, by dissolving the polyethylene O sulfoxide (POE) orthophosphoric acid H ₃ P 0 ₄ in, it is possible to obtain a proton conductor acidic, not yet to achieve a sufficiently high conductivity. Conventional proton conduction is mainly due to acid dissociation, which requires water or high temperature. In contrast, basic compounds such as imidazole and pyrazole have been found to conduct protons at a relatively low temperature under anhydrous conditions, and a completely new proton conductor has been proposed. High proton conduction has also been observed in salts based on this (ImZHTFSI, etc.). The imidazole salt is It shows conductivity 14 even in crystalline solids, and may show higher conductivity in the temperature range above the melting point, and is considered to have proton self-dissociation properties (KD Kreuer Solid State Ionics, vol. 94, para. 55, 1997). It has also been reported that the addition of imidazonole to a complex of imiggunnole derivative and zirconium phosphate improves conductivity (M. Casciola et al., Solid State Ionics, 35, 67, 1991). It has long been known that a complex of a base and a protonic acid exhibits high proton conductivity, such as the amine base triethylenediamine hexamethylenetriamine.

It has been reported in 1976 that iO coalescence shows proton conductivity (T. Takahashi et al., Solid State Chem., vol. 17, paragraph 353, 1976).

 Some of these proton exchangers exhibit properties of an ionic liquid. An ionic liquid is a substance composed of only ions having a melting point at a temperature close to room temperature, and is a stable liquid having a small vapor pressure over a wide temperature range. 1992 Wilkes et al. Discovered an ionic liquid that is stable against air and water (JS Wilkes et al., Cliem. Commun-, p. 965, 1992). As a solvent completely different from the molecular liquids described above, it has been studied to apply it as a Green Solvents for realizing Green Chemistry, such as solvents and catalysts in organic synthesis and polymer synthesis (T. Welton, Chem. Rev. 99, 2071, 1999).

 In addition, since ionizable liquids can be freely created by combining ions according to the purpose, they are also called Designer Solvents (M. Freemantle, Chem. & Eng. News, May 15, Issue 37, Item 37, year 2000).

 Since ionic liquids are ionic conductors, have excellent reduction resistance, high decomposition voltage, excellent safety, and exhibit liquid properties over a wide temperature range, secondary batteries (RT Carlin et al., J. Electrochem. Soc, 141, L73, 1994), electric double layer capacitor (C. Nanjimdiah et al., J. Electrochem. Soc., 144, 3392, 1999), dye-sensitized solar cell (N. Papageorgiou et al.) J. Electrochem. Soc, Vol. 143, pp. 3099, 1996).

JP 2000-50811 discloses a binary mixture of certain nitrogen bases belonging to the azole series and acid addition salts of these nitrogen bases. It has been shown to be an electron conductor, and its application to electrochemical devices such as displays has been proposed. Further, JP-T-2000-517462 discloses a proton conductor which is an acid and a non-aqueous amphoteric material. However, there is no specific disclosure in these publications as a proton exchange membrane suitable for a proton exchanger for a fuel cell, and it is difficult to use it as a fuel cell membrane. Published Japanese Translation of PCT International Publication No. 2000-517462 suggests the application of ionic liquids to fuel cells. However, there is no disclosure of any embodiment and performance such as a specific configuration and a usage method as a fuel cell membrane.

In the following, examples of ionic liquids exhibiting liquid properties over a wide temperature range by combinations of various cations and anions will be described.

イオン性液体の主な特徴としては、 以下の様なものが挙げられる。 1 ) 液体であるが高温においても蒸気圧を示さない （不揮発性)。

The main features of the ionic liquid are as follows. 1) Liquid but does not exhibit vapor pressure even at high temperatures (non-volatile).

 2) Some have low freezing points and do not freeze even at -80 ° C.

 3) It is nonflammable.

 4) Many are chemically stable.

5) Polymer-in-salt type solid electrolyte is formed by addition of polymer. By taking advantage of these characteristics of ionic liquids, it is possible to replace ionic conduction in a wide temperature range. Can be realized.

For example, a high-temperature proton conducting membrane in which an ionic liquid is incorporated into a fluorine-based ion exchange membrane (M. Doyle et al., J. Electrochem. Soc., 147, 34, 2000) has been reported. The presence of water is necessary because the salt itself has no proton exchange capacity. In normal temperature molten salt complexed by a fluorine-based ion exchange film typified by Nafuion (TM) system, the improvement of ion conductivity even at low temperatures is observed ^{(0 ° C: lxl 0- 3} SZ cm, the Nafuion system 100 times or more).

Also, in ionic liquids, it is generally thought that a protonated nitrogen-based substance can transfer protons to a non-protonated nitrogen-based substance, thereby enabling proton transfer in a medium. Have been. For example, in a binary mixture of I imidazole and HBF _4, and constitute anhydrous proton conductor, compatible 1 "raw water is high Imidazonore I formidacillin sledding © beam triflate (Monore ratio 3: 1). A two If the original mixture, conductivity 10- S at 25 ° C - constituting ¹ 'cm- ¹ over anhydrous proton conductor neutral.

 As described above, ionic liquids composed of a proton exchanger such as imidazole or a salt thereof exhibit high proton conductivity in an anhydrous state, but are often highly compatible with water. In a proton exchange membrane impregnated with water, there is a problem that a proton exchange component is eluted by water generated by a force source. Therefore, these currently proposed proton exchange membranes could not be used as components of fuel cells.

 The present inventors evaluated a mixed film of a room-temperature molten salt and a fluorine-based ion exchange membrane represented by Nafion (trademark) in a fuel cell system. The non-humidifying operation time after stopping humidification is more than 4 times, and it is found that the molten salt has the effect of trapping water in the film. However, water is deeply involved in proton conduction and does not exhibit proton conduction in the absence of water.

The present invention has been made in view of the above situation, and its main purpose is to express high proton conductivity without depending on the presence of water and to produce water in a cathode. Fuel cell proton exchanger which is suitable for use as a proton exchanger for fuel cells, and a fuel cell using the same. To provide a pond.

 BRIEF DESCRIPTION OF THE FIGURES

 FIG. 1 is a phase diagram of an ionic liquid in which benzimidazole (BI) and HTFSI are mixed in various combinations in one embodiment of the present invention.

 Figure 2 shows the Arrhenius plot for a mixture of BI and HTFSI at various monole ratios.

 FIG. 3 is an explanatory diagram showing a schematic configuration example of a ionic liquid conductivity measuring cell (AC impedance method) used in the proton exchanger for a fuel cell according to the present invention. FIG. 4 is an explanatory view showing another example (DC four-terminal method) of a cell for measuring the conductivity of an ionic liquid used in a proton exchanger for a fuel cell according to the present invention.

 FIG. 5 is a graph showing the temperature dependence of the proton conductivity obtained by the AC impedance method and the DC four-terminal method for the BI / HTFSI molar ratio of 812. FIG. 6 is an explanatory diagram showing a schematic configuration of a simple fuel cell using an ionic liquid as a proton exchanger.

 FIG. 7 is a graph showing current-voltage characteristics when a simple fuel cell uses a BI / HTFSI mixed solution having a molar ratio of 8/2 as an electrolyte.

 FIG. 8 is an explanatory diagram showing, in order from the top, a proton conduction mechanism when using water, an explanatory diagram showing a proton conduction mechanism when using a normal ionic liquid containing imidazole (Im), and the present invention. FIG. 2 is an explanatory diagram showing a proton conduction mechanism when an ionic liquid containing benzoimidazole (BI) according to one embodiment is used.

 FIG. 9 is a graph showing an example of the change over time of the open electromotive force (OCP) when a constant flow rate of ¾ and air are circulated under a predetermined temperature condition in the fuel cell according to one embodiment of the present invention. .

 FIG. 10 is a graph showing thermal analysis data of a BI / HTFSI mixed solution with various molar ratios.

 FIG. 11 is a graph showing the results of ^ H-NMR analysis performed on 8 liquid [ion liquids] / 4 liquid BI / HTFSI with a molar ratio of 8/2.

FIG. 12 is a graph showing current-voltage characteristics when a simple fuel cell uses Im / HTFSI having a molar ratio of 5/5 as an electrolyte. Disclosure of the invention

 The present inventors have conducted intensive studies to solve the above-mentioned drawbacks, and as a result, a wide variety of proton exchangers using a certain type of ionic liquid and complexes of the proton exchangers with the polymer matrix have been widely used. The present inventors have found that a high proton conductivity is exhibited in the temperature range without depending on the presence of water, and that an excellent proton exchanger for a fuel cell is provided, and the present invention has been completed.

 That is, the proton exchanger for a fuel cell of claim 1 is characterized by containing at least one kind of basic compound containing a hetero atom in order to solve the above-mentioned problems.

 According to the above configuration, the compound containing the basic compound as a constituent component has a low melting point and can realize a high proton conductivity, so that it exhibits high protein conductivity without depending on water. In addition, it is possible to provide a proton exchanger that is insoluble in water generated at the cathode and can be suitably used as a proton exchanger for a fuel cell.

 In order to solve the above problems, in the proton exchanger for a fuel cell according to claim 2, the basic compound forms part or all of the components of the ionic liquid; It is characterized by being dissolved.

 According to the above configuration, since the ionic liquid has a low melting point and a high proton conductivity, the ionic liquid exhibits high proton conductivity without depending on the presence of water and generates at the cathode. Provided is a proton exchanger which is insoluble in water and can be suitably used as a proton exchanger for a fuel cell.

 In order to solve the above problems, the proton exchanger for a fuel cell according to claim 3 is characterized in that the proton exchanger contains a hydrophobic ionic liquid.

 According to the above configuration, the hydrophobicity of the ionic liquid can suppress elution of water generated at the cathode, so that it is possible to provide a proton exchanger more suitable for a fuel cell. it can.

In order to solve the above-mentioned problems, the proton exchanger for a fuel cell according to claim 4 is characterized in that the proton exchanger has an interaction between an ionic liquid and a polymer matrix and an ion exchange liquid. It is characterized in that a gel is formed by utilizing the function of the ionic liquid as a crosslinking point.

 According to the above configuration, the flowability can be controlled by forming the gel, so that the outflow of the ionic liquid as a component of the membrane can be controlled. Furthermore, hydrophobicity can be imparted by the interaction between the ionic liquid and the polymer matrix.

 In order to solve the above-mentioned problems, the proton exchanger for a fuel cell according to claim 5 is characterized in that the polymer matrix has an ion exchange ability.

 According to the above configuration, the proton conductivity can be further increased by the ion exchange ability.

 In order to solve the above-mentioned problems, the proton exchanger for a fuel cell according to Claim 6 is characterized in that the content of the polymer matrix is in the range of 3 to 20% by weight. When the content of the polymer matrix is too small, it is difficult to form a self-retaining gel, whereas when it is excessive, the proton conduction is sharply reduced. According to the above configuration, it is possible to form a membrane with a much smaller amount of polymer than in a normally used proton exchange membrane, and a high proton conductive membrane can be obtained.

Fuel cell proton exchange body according to claim 7, in order to solve the above problems is characterized in that the hydrogen gas permeability of the pro ton exchangers 2x10- ⁴ cm ³ cm- ¹ s is one ^{of 1} or less . If the hydrogen gas permeability 2x10- ³ cm ³ cm- ¹ s- ¹ or more leads to a reduction in the output of the fuel cell. The hydrogen gas permeability is preferably

One is ^one . According to the above configuration, it is possible to suppress a decrease in the fuel cell output due to the crossover of (1).

In order to solve the above problems, the proton exchanger for a fuel cell according to claim 8 is characterized in that it has a proton conductivity of 2xl (T ⁴ S / cm or more) at room temperature and in a non-humidified state.

 According to the above configuration, it is possible to provide a fuel cell proton exchanger that exhibits high proton conductivity without depending on the presence of water and is insoluble in water generated at the cathode. it can.

The proton exchanger for a fuel cell according to claim 9 has the following object to solve the above problems. At a temperature of 0 ° C or more, it exhibits a proton conductivity of 1 xlO- ² SZcm or more in a non-humidified state.

 When this proton exchanger is used, water generated in the fuel cell power source is scattered by gas and dissipates, and the proton exchanger exhibits high proton conductivity irrespective of the presence of water. Since the salt constituting the body has excellent thermal stability, a stable and high-performance fuel cell can be provided.

 In order to solve the above-described problems, the proton exchanger for a fuel cell according to claim 10 is characterized in that its constituent components are water-insoluble.

 According to the above configuration, since the components of the proton exchanger are insoluble in water, the components of the proton exchanger do not elute into water due to the presence of water generated by the cathode. Therefore, the life of the fuel cell can be greatly extended.

In order to solve the above-mentioned problems, the proton exchanger for a fuel cell according to claim 11, comprising a basic compound containing a hetero atom and an acid containing a fluorine atom and a sulfur atom in a molecule. It is a salt, and the molar ratio of the acid is in the range of 0.9 to 1.1 based on the basic compound.

 According to the above configuration, since the constituent components of the proton exchanger are thermally stable, a high-performance fuel cell that is stable even at high temperatures can be provided.

 A fuel cell according to claim 12 is configured to include the proton exchanger according to any one of claims 1 to 11.

 According to the above configuration, it is possible to provide a fuel cell excellent in long-term high-temperature stability without depending on water, without elution of components to water, based on the above-described excellent properties of the proton exchanger. .

 Hereinafter, the present invention will be described in more detail with reference to the drawings.

 The proton exchanger for a fuel cell of the present invention contains a basic conjugate containing at least one kind of hetero atom.

Examples of the basic compound containing at least one hetero atom used in the present invention include a linear basic compound and a cyclic basic compound exemplified below. It suffices that at least one kind of hetero atom is contained, and the number of kinds is not particularly limited, but it is more preferable that at least two kinds of N atoms are contained. Examples of the linear basic compound include butylamine, triethylamine, dibutylamine and the like.

 Examples of the cyclic basic compound include, for example, ataridine, benzothiazole, benzoimidazonole, 1,2,3-benzotriazonole, carbazole, cinnoline, dibenzofuran, 1,10-phenoantholine, phenothiazine, flavone, quinoline, Isoquinoline, coumarin, pudding, benzofuran, indole, thonaphthalene, s-triazine, s-trithiane, pyriazine, pyrimidine, 1,3,4-thiadiazole, 4H-pyran, pyridine, imidazole, pyrazonole, 1,2,3- Triazole, 1,2,4-triazole, 1,2,3-oxaziazole mono, oxazonole, thiazonole, pyrazine, pyrene, pyridazine, piperidine and derivatives of the above-mentioned cyclic basic compounds, 2-pyrazolin , Virazolidin 3-pyrroline, pyrrolidine, 1,3-dioxolane, cyclopentane, furan, pyrrole, p-dioxane, monoreforin, quinoxaline, 4,4'-trimethylenedipyridine, piperazine, 4,4'- Trimethylene dipiperidine, hydrazine, 1- (3-aminopropynole) -imidazonole, 1,3,5-triazole, diphenylamine, triphenylamine, steroid ring compounds and the like.

 The linear basic compound and the cyclic basic compound exemplified above may be used alone or in combination of two or more as necessary.

 Among the basic compounds exemplified above, pyrazole, 2-pyrazolin, virazolidine, imidazole, 1,2,3-oxaziazole, 1,2,3-triazole, 1,2,4-triazole, 1,3,4-thiadiazonolone , Pyridazine, pyrimidine, pyrazine, piperazine, 1,3,5-triazine, benzimidazole, purine, sinoline, quinoxaline, 1,10-phenanthroline, pyridine, pyrrolidine, triethylamine, etc. S, thermal stability, hydrophobicity It is even more preferable because it is superior to others.

The basic compound used in the proton exchanger for a fuel cell of the present invention has a proton exchange ability, and may form part or all of the components of the ionic liquid, or may be dissolved in the ionic liquid. preferable. Proton exchange of the basic compound according to the present invention The exchangeability will be described later.

 Some of the ionic liquids are liquid at a relatively low temperature and are called room temperature molten salts. Some substances are composed only of ions having a melting point at a temperature below room temperature. In recent years, it has been attracting attention as a solvent completely different from molecular liquids such as water and organic solvents, since it is composed only of ion. The temperature range of the property of the ionic liquid is mainly determined by the structural distortion caused by the asymmetric structure of the organic cation. Many materials can be designed because asymmetric force thiones such as imidazolyme, pyridinium, ammonium, and phosphonium are organic materials.

 Examples of the acid for forming the ionic liquid according to the present invention include, for example, trifluorosulfonic acid (triflic acid), bisfluorinated sulfonimide, bistrif / remethod, romethansnorehonimid, and bistrifonole. Such as methanesulfonylmethane, tristrifluoromethane-snolephonylmethane, and trisfluorosulfonylmethane. Of these, preferred are bisfluorosulfonimide and bistrifluoromethanesulfonimide. As shown in Table 1, various combinations of cations and ayuons indicate liquids over a wide temperature range.

Examples of the proton-conductive ionic liquid (room-temperature molten salt) include benzoimidazolium bis (trifluoromethanesulfonyl) imide (BI / HTFSI) represented by the following chemical formula (1). The present invention is not limited to this, and is constructed as a low-melting ionic liquid by combining the above-exemplified basic compound and the above-exemplified acid and the like in a predetermined molar ratio and subjecting them to an acid-base reaction. .

10 o. Proton conductors used in fuel cells operated in a non-humidified state above c include pyrrolidine, pyridine, piperidine, triethynoleamine, imidazonole, pyrazonole, pyrazine, 1,2,4-triazole, butynoleamine , Dibutynoleamine, diphen-lamine, benzimidazolone, morpholine, quinoxaline, 4,4'-trimethylenedipyridine and a basic compound selected from the group consisting of bisfluorosulfonimide and / or its derivatives. A salt with an acid, The molar ratio is from 0.9 to 1.1, preferably from 0.95 to 1.05, based on the former. Outside this range, it is preferable that fuel cell characteristics cannot be obtained. Particularly preferred basic conjugates are pyrrolidine, pyridine, piperidine, triethynoleamine, imidazole, and virazo ^ pyrazine 1,2,4-triazolone.

 FIG. 1 is a phase diagram in the case where benzoimidazole (BI) and bis (trifluoromethanesnorephonyl) amide (HTFSI) are mixed in various combinations. As shown in the figure, when BI and HTFSI are equimolarly mixed, an acid-base neutralization reaction is caused to form a salt. The present inventors have confirmed that an equimolar mixture of BI and HTFSI forms a neutralized salt (melting point 117.5 ° C). Above the melting point, the equimolar mixture exhibits the high temperature thermal stability characteristic of ionic liquids. Also, by appropriately adjusting the composition of HTFSI with respect to BI, a low-melting ionic liquid can be obtained, which can be used as a proton-conducting medium. The inventors have also confirmed that a BI / HTFSI molar ratio of 812 forms a eutectic mixture (melting point 98 ° C.).

 As described above, the concept of the ionic liquid used in the proton exchanger for a fuel cell of the present invention is to design a liquid substance having a low melting point by an acid-base reaction by setting a molar ratio and use this as a proton conductive medium. There is a feature in the point. In this regard, the design of the ionic liquid according to the present invention reduces the Coulomb interaction (ΔΗπι) to lower the melting point (Tm) and reduces the entropy (ASm) as shown in the following equation. It is different from the basic idea of ionic liquids, such as increasing the basic idea.

 Tm = AHm / ASm

 FIG. 2 is an Arrhenius plot when, for example, BI and HTFSI are mixed at various molar ratios. From FIG. 2, it can be seen that the mixture is in a molten state at 130 ° C. or higher and exhibits high proton conductivity.

 Since the ionic liquid constructed as described above has a hydrophobic property, it is not easily eluted even by the presence of water generated during the operation of the fuel cell. The hydrophobicity of the ionic liquid of the present invention is confirmed, for example, by stirring the ionic liquid with water and then performing phase separation.

Next, the operation check of the ionic liquid BI / HTFSI in the fuel cell system will be described. FIG. 3 is an explanatory diagram showing a schematic configuration example of a cell (AC impedance method) for measuring the conductivity of ion-free liquid used in the proton exchanger for a fuel cell of the present invention. FIG. 4 is an explanatory view showing another example (DC four-terminal method) of a cell for measuring the conductivity of an ionic liquid used in the proton exchanger for a fuel cell of the present invention.

In either measurement method, when a platinum electrode is immersed in an ionic liquid and hydrogen and nitrogen are blown into one electrode, the current value can hardly be confirmed under a nitrogen atmosphere, whereas the current value can be hardly confirmed under a nitrogen atmosphere. In, the current value is proportional to the senor voltage, and bubbles are confirmed at the counter electrode. This confirms that a fuel cell reaction occurs at the anode (the working electrode that has undergone H ₂ flow). This result means that the BI / HTFSI composite exhibits proton conductivity and that it exists as an electrode active material in the strong S Pt electrode and the BI / HTFSI composite electrolyte solution. I taste. Also, from the linearity of the current value with respect to the cell voltage, equilibrium is established in the BI / HTFSI complex IH ₂ | Pt, and a stable potential as a hydrogen electrode is given. The electrode reactions at the anode and at the force sword

Anode H ₂ + 2 BI → 2 BI-H ⁺ + 2 e

Force Sword 2 BI-H + + 2 e— → 2 BI + H ₂

It is considered that active protons on and between the electrodes exist in the form of BH ⁺ . When hydrogen was flowed to the anode and oxygen was flowed to the power source, an open circuit voltage (OCV) of 0.75 V was obtained.

From this, when O ₂ gas flows in the power sword,

Anode + 2 BI → 2 BIH ⁺ + 2e ~

Force Sword 2BIH + + 1/20 ₂ + 2e— → 2BI + H ₂ O

It can be confirmed that the reaction continues stably and exhibits the function as a fuel cell.

Figure 5 shows the AC impedance method (shown as “Α · C. Impedance method” in the figure) and the DC four-terminal method (shown in the figure) for the complex with a BI / HTFSI molar ratio of 8/2. This is a graph showing the temperature dependence of the proton conductivity determined by “DC 4-probe methodj.” The ratio of proton conductivity to the total ionic conductivity is about 0.75 to 0.85. Yes, the main conductive carrier in this system Is clearly a proton.

 FIG. 6 is an explanatory diagram showing a schematic configuration of a simple fuel cell using an ionic liquid as a proton exchanger (electrolyte).

 FIG. 7 is a graph showing current-voltage characteristics when a BI / HTFSI composite having a molar ratio of 8/2 is used as the electrolyte in the simple fuel cell shown in FIG. It can be seen from this Darafka et al. That the reaction at the anode and the power source proceeds steadily and the basic operation of the fuel cell under non-aqueous conditions can be confirmed.

That is, as is apparent from FIG. 7, the simplified cell is opened electromotive force 0.75 V, since the shown circuit current 70Myuarufa, when the flow of the 0 ₂ gas in a force Sword, anode H ₂ + ₂ BIm → 2 BImH ⁺ + 2e—

Force Sword 2BImH ⁺ + 1/20 ₂ + 2e- → 2BIm + H ₂₀

It can be confirmed that the reaction continues to occur stably and the function as a fuel cell can be exhibited.

 FIG. 12 is a graph showing the current-to-current characteristics at the 130 port when Im / HTFSI having a molar ratio of 5/5 is used as the electrolyte in the simple fuel cell. From this graph, it can be seen that the reaction at the anode and the power source proceeds steadily, and the basic operation of the fuel cell under non-aqueous conditions can be confirmed.

 The proton exchanger of the present invention is useful as a gel electrolyte or a polymer electrolyte. The embodiment of the proton exchanger for a fuel cell of the present invention is not particularly limited, and is appropriately selected as needed. The embodiment may be, for example, a proton exchange membrane formed in a film shape or a simple structure using a U-shaped tube filled with an ionic liquid.

 The polymer-in-salt polymer solid electrolyte is a function-separated solid electrolyte in which the ionic liquid is responsible for the electrolyte ionic conductivity and the polymer is responsible for the mechanical properties. Watanabe, proposed by Angell et al. (Watanabe et al., JCS Chem. Comrmm., P. 929, 1993), (CA Angell et al., Nature, 362, 137, 1993). This concept is also valid for proton conductors.

These ionic liquids used in the proton exchanger for a fuel cell of the present invention include a specific matrix component (monomer, oligomer or polymer) and a polymer-in-salt. It is possible to form a gel electrolyte. This Polymer-in-Salt type gel electrolyte is characterized in that the proton exchange membrane forms a high-strength self-retaining genole between the salt and the polymer matrix.

 髙 The molecular matrix is not limited as long as it can solid-state the room temperature molten salt into a film or a cast product, but is preferably a synthetic polymer compound. Specific examples of the synthetic high molecular compound include polyvinyl high molecular compounds such as polyvinyl chloride, polyacrylonitrile, polymethyl methacrylate, and polyvinylidene fluoride; polyoxymethylene, polyethylene oxide, and polypropylene oxide. Ether-based polymer compounds; polyamide-based polymer compounds such as nylon 6 and nylon 66; polyester-based polymer compounds such as polyethylene terephthalate; polycarbonate-based polymer compounds; ionene-based polymer conjugates; It is. As the synthetic polymer compound, polyacrylonitrile, polyether and the like are preferable. Further, it is also preferable that the polymer matrix such as polystyrene sulfonic acid and perfluorosulfonate molecule have an ion exchange ability. Furthermore, it is also possible to form a film by crosslinking these polymerizable precursors, for example, polymerizable conjugates such as acrylate.

The mixing ratio of the room temperature molten salt and the polymer matrix is not limited as long as it is within the range of mutual compatibility. The compounding ratio of the two is preferably in the range of 3 to 20% by weight, more preferably in the range of 5 to 15% by weight, based on the weight of the molten salt at room temperature. More preferably, it is in the range of 7 to 12% by weight. When the content of the polymer matrix is less than 3% by weight, it is difficult to obtain a useful gel, whereas when it exceeds 20% by weight, the conductivity decreases. If there is no ionizing group in the polymer Ma Torikusu is 1 2 weight content of the polymer matrix ⁰ /. It is preferable to set the following. The hydrophobic property, which is an important property of the proton exchanger of the present invention, can be realized by the type of salt formed by a combination of a base and an acid that form an ionic liquid, the form of a gel that forms a matrix, and the like.

Considering the morphology of the gel that forms the matrix, a hydrophobic polymer matrix may be effective in some cases. As a specific method of forming the polymer matrix, a polymer compound is directly heated and dissolved in the above-mentioned room temperature molten salt and cooled. It is obtained by mixing the two in an appropriate organic solvent or by shaping, and then distilling off the solvent by a method such as drying under reduced pressure. In addition, it is also possible to obtain a polymer conjugate by polymerizing a monomer in the molten salt.

Such proton exchange membrane at room temperature and non-humidified state, to have a proton conductivity on 2x10- ⁴ S / cm or more is determined.

 Here, “room temperature” refers to a temperature of about 20 ° C to less than 100 ° C. In addition, the “non-humidified state” is different from the “humidified state” in which the humidity is near 100% by a humidifier or the like, and humidifies any gas from a commercially available air (or oxygen) cylinder or a commercially available hydrogen cylinder. Refers to the state of being used.

The hydrogen gas permeability of the proton exchange ^{membrane, 2x10- 4 cm 3 cm- 1 s-} 1 or less der Rukoto is required, in order to realize this, H _2, 0 ₂ to ionic liquids Low solubility is required. In the present invention, the components of the proton exchanger for a fuel cell preferably do not elute due to the presence of water, that is, are preferably water-insoluble. In other words, in order for the proton exchanger to show hydrophobicity, it is necessary that the room-temperature molten salt is hydrophobic, that the basic compound is hydrophobic, that the matrix is hydrophobic, or that two or more of these are used. Is realized by a combination of

 FIG. 8 shows, in order from the top, the proton conduction mechanism when using water, a normal ionic liquid containing imidazole, and an ionic liquid containing benzoimidazole according to an embodiment of the present invention, respectively. FIG.

Nafuion using water as a proton-conducting medium; proton conduction (trade name fluorinated ion exchange membrane), the humidity dependency is high, the proton conductivity at a relative humidity of 3% is about 2x10- ⁵ S / cm, also, In a temperature range of 70 ° C or higher, the proton conductivity sharply decreases due to evaporation of water. Furthermore, in the low-temperature and low-humidity region, improvement in proton conductivity by more than three orders of magnitude is desired.

In other words, the proton conduction mechanism of naphth ions is a mechanism in which water is used as the proton conduction medium, as shown in the upper diagram in FIG. That is, first, neutral H ₂₀ accepts a proton and dissociates the proton of the sulfonic acid group immobilized on the polymer. H ₂ 0 is protonated to 0+, and proton exchange occurs between H ₃ 0 ⁺ and ¾0, so that ¾0 acts as a medium for transporting protons Will be.

The Grotthuss Mechanism, in which protons (H ⁺ ) hop between protonated and positively charged hydronium ions (H ₃₀ +) and neutral H ₂ O, and the proton donor H ₃ It is thought that both the O ⁺ and the vehicle mechanism, which is the proton conduction by molecular diffusion of the proton acceptor H ₂ 0, express proton conduction (KD Kreuer, Chem. Mater., 8 vol. 610, 1996).

Considering the charge, the reaction using Naphion® is a proton exchange reaction between neutral H ₂₀ and the monovalent cation H ₃₀ ^+, and the exchange reaction is rapid. And the following equilibrium equation holds.

H ₂ 0 + H + <~~> H ₃ 0 ⁺

 The present inventors have focused on the fact that the presence of water in a naphthion membrane acts as a base for protons, and found that various ionic liquids are useful as a proton-conducting medium (see FIG. 8, middle diagram). ), A proton exchanger incorporating the water-insoluble (water-insoluble) ionic liquid, which shows the properties of the liquid over a wider range, into the basic structure (lower figure in Fig. 8) Force S Excellent as a proton exchanger for fuel cells Was found. In other words, the fact that water can be used in a temperature range where it is impossible to use water as a proton conducting medium, and that a hydrophobic ionic liquid is excellent as a proton exchanger for fuel cells. I found it.

 BEST MODE FOR CARRYING OUT THE INVENTION

 Hereinafter, the ability to explain the present invention in more detail by showing examples The present invention is not limited to these examples.

 The various measurement techniques in the examples are as follows.

<Confirmation of hydrophobicity of ionic liquid>

 The hydrophobicity of the ionic liquid was confirmed by mixing and stirring the ionic liquid and water, followed by phase separation.

Confirmation of hydrophobicity of proton exchange membrane>

The hydrophobicity of the proton exchange membrane was confirmed by the fact that the ionic liquid did not elute after mixing and stirring the ionic liquid and water. Creating a fuel cell>

 The fuel cell using the ionic liquid was made through the following steps 1-4.

1. Preparation of catalyst electrode

* Materials used

 (a) Carbon paper (SGL Carbon Japan)

 Features Conductive, water repellent

 (b) Catalyst Pt / C (40wt% platinum supported carbon, Tanaka Kikinzoku)

(c) a binder one per full O b sulfonic acid polymer solution (trademark "Nafion", a solid concentration of 20wt%, n-PrOH (0-60 %)) EtOH (0-60%), H 2 O (0 -30%) etc.), volatile organic matter (about 5%))

 2. Preparation of catalyst paste

Zr0 ₂ balls media 3mm diameter in 150ml containers for a hybrid mixer (20.9 g), placed in n-BuOH (5.4 g) and 20 wt% Nafion solution, there was added portionwise Pt / C (1.35g) (catalyst) Was. Furthermore, after adding 3 nm ₂ diameter Zr02 balls (20.9 g), the whole was blended. Put the lid on the container, put it in a hybrid mixer (KEYENCE, “HM-500”), set the revolution at 2,000 rpm and the rotation at 800 rpm, mix and stir for 10 minutes, and then perform defoaming treatment for 30 seconds. after uniformly dispersed, to obtain a catalyst paste by separating the catalyst paste and Zr0 ₂ balls. The obtained paste was stored in a closed container to prevent evaporation of the solvent.

 3. Preparation of catalyst layer

A weighed carbon paper (56 mm X 56 mm) was placed on a printing table (suction possible). The printing screen was lowered, and the catalyst paste was dropped on the screen to perform printing. This printing was repeated until the applied catalyst base reached a predetermined weight. When the weight reached a predetermined value (in terms of platinum weight: 0.5 mg / cm ² ), the printing layer on the carbon paper was dried by 8D drying.

 4. Cell assembly

 Here, the configuration of the cell was as follows.

Current collector / separator (with carbon electrode and gas flow path) / carbon paper / MEA / silicone sheet / separator / current collector <Method for measuring hydrogen gas permeability of proton exchange membrane>

H ₂ gas cross over has a large effect on electromotive force. Therefore, an evaluation of the H ₂ gas permeability of the proton exchange membrane and also of the MEA is required. The cell used for the measurement was a test cell, with a proton exchange membrane interposed, H ₂ gas flowing through one side, and N ₂ gas flowing through the other electrode at a predetermined flow rate. _The amount of ¾gas contained in the _two gases was quantified by gas chromatography and estimated.

Power generation test>

The power generation experiment was performed using the fuel cell prepared above. Figure 9 shows an example of the change over time of the open electromotive voltage (OCV) when a constant flow of H ₂ gas and Air is flowed at a constant temperature. In FIG. 9, the electromotive force E (indicated by V) is indicated on the left ordinate, and the time (indicated by seconds = s) is indicated by a mark. '

Proton conductivity measurement>

 The proton conductivity (σ / Scm—) was measured using a simple fuel cell shown in FIG. 6 described above, using a hydrogen reversible electrode direct current four-terminal measuring device (“Solartron 1255B”, Solartron®).

 Measurement of heating stability)

 The heating stability was measured by a thermogravimeter and indicated at a temperature at which the weight at room temperature was reduced by 10% by weight.

Example 1

 142 g of benzoimidazole (BI) and 8.43 g of bis (trif-noreomethanesulfonyl) amide (HTFSI) were weighed in a glove box (2) in an argon atmosphere, mixed, heated and melted to make them homogeneous.

 The heat resistance of the obtained ionic liquid was evaluated by differential scanning calorimetry and thermogravimetry. The melting point (° C) was measured at a heating rate of 10 ° C / miri using a differential scanning calorimeter (“DSC 220”, manufactured by Seiko Ichi Electronics Co., Ltd.). The graph of the thermal analysis result is shown in FIG.

In the case of an equimolar mixture of BI and HTFSI, a crystalline salt was formed, the melting point of which was 117.5 ° C. Atsuta excellent liquid thermal stability of non-volatile to around 370 ^e C. The mixture having a molar ratio of 8: 2 formed a eutectic mixture having a melting point of −6 ° C. Molar ratio 8: 2 Fig. 11 shows the results of ¹ H-R analysis of the ionic liquid BI / HTFSI.

 Next, the operation of the simple fuel cell was confirmed using the ionic liquid having a molar ratio of 8: 2 adjusted by the above operation. Figure 7 shows the current-potential curve when hydrogen flows through the anode and oxygen flows through the cathode. As is evident from Fig. 7, the open-circuit power was 0.75 V and the short-circuit current was 70 µm.

 Next, a proton exchange membrane was prepared using the ionic liquid. Electrolyte solution (BI / HTFSI = 8: 2 (molar ratio)) 10 g of vinyl monomer methyl methacrylate (MMA) 2.0 g, crosslinker ethylene glycol dimethacrylate E GDMA 0.04 g, and polymerization initiator (AIBN) The solution to which 0.03 g was added was injected between opposed glass plates via a spacer (thickness: 0.5 mm), and then heated to allow the radical polymerization reaction to proceed to obtain a conductive proton exchange membrane. .

The resulting proton exchange membrane exhibited a conductivity of 2.8 × 10—sScm- ¹ . Further, by ₂ gas permeability 'measuring method of above, was measured hydrogen permeability at 130 ° C, it was about 1.6x10 one ⁴ cm ³ cm one ¹ s one ^1. When the hydrophobicity (water affinity '(4)) of the obtained proton exchange membrane was confirmed by the above method, it showed a high degree of hydrophobicity.

 The results of Example 1 and the following Examples 2 to 12 and Comparative Example 1 are summarized in Table 2 below.

Example 2

 The same operation as in Example 1 was performed except that 2-methylbenzotriazole (MBT) was used instead of BI, to prepare an ionic liquid, a proton exchange membrane using the ionic liquid, and a simple fuel cell.

The obtained proton exchange membrane exhibited a conductivity of 3.3 × ^{10 3} ScnT ^{1 under} the following conditions. Also, as a result of the H ₂ gas permeability measurement method Yore, Te measured hydrogen permeability of about 1.7 × 10 - ⁴ in cm ³ cm one ¹ s one 1 fe ivy.

Example 3: L 0

Instead of BI, 1,2,4-triazole (Tr), pyrazine (PZN), quinoxaline (QXL), diphene / reamine (DPA), 4,4, -trimethylenedipyridine (TMDP), pyrrolidine (PLD) ), Pyridine (PD) or triethylamine (TEA), respectively. An ionic liquid, a proton exchange membrane and a fuel cell using the ionic liquid were prepared in the same manner as in Example 1 except that they were weighed and mixed so that the molar ratio with HTFSI was 5: 5. .

Example 11: L 2

 Instead of BI, use a mixture of BI or MBT and 2-butyl-4-methylimidazole (BMI) in an equimolar ratio, weigh so that the mixture and the HTFSI have a monolith ratio of 2: 1, Except for mixing, the same operation as in Example 1 was performed to prepare an ionic liquid, a proton exchange membrane using the same, and a fuel cell.

Comparative Example 1

The same operation as in Example 1 was performed except that imidazole (Im) was used instead of BI, to prepare a comparative proton exchanger using an ionic liquid having an Im TFSI molar ratio of 2: 8. The proton exchanger exhibited a conductivity of 5.0x10-3 Scm- ¹ at 80 ° C. Further, by the method of the hydrogen gas permeability measurement, was measured for the hydrogen permeability of comparative proton exchanger was about 2.0x10 one ^{4 cm 3 cm- 1 s _ 1} .

Table 2

As is evident from Table 2, the ionic liquid according to the present invention has a low melting point and a sufficient proton conductivity at 130 ° C. In addition, the proton exchange membrane in which a gel was formed by such an ionic liquid and a polymer matrix shows good hydrophobicity with respect to the degree of misalignment, and can be used as a proton exchanger for a fuel cell. In Examples 3, 4, 8 to 10, the hydrophobicity of the ionic liquid was low, but when a proton exchange membrane was formed together with the high molecular weight matrix, sufficient hydrophobicity was exhibited. It can be seen that it can be used as a proton exchanger for fuel cells.

Example 13-20

 Instead of BI, use pyrrolidine, pyridine, piperidine (PPD), triethylamine, imidazole, pyrazole (Py), pyrazine (PRD) or 1,2 triazole (Tr), respectively, and the molar ratio with HTFSI is 5: 5. The respective salts were synthesized in the same manner as in Example 1 except that the salts were weighed and mixed so that the heating stability of these salts was measured. Table 3 shows the results.

The results shown in Table 3 show that these salts have excellent power!] Thermal stability, and ionic liquids and proton exchange membranes using them have proton conductivity, hydrophobicity, and low hydrogen permeability. Is shown. Therefore, it is clear that a high-performance fuel cell can be obtained when the ionic liquid using the salt prepared in Examples 13 to 20 and the proton exchange membrane are used.

Industrial applicability

The proton exchanger for a fuel cell according to claim 1 contains at least one hetero atom. Contains basic compounds.

 The compound containing the basic compound as a constituent has a low melting point, is insoluble in water, and has a high proton conductivity, so that it exhibits high proton conductivity without depending on the presence of water. . Therefore, it is possible to provide a proton exchanger for a fuel cell which is not dissolved by water generated in a power source of the fuel cell.

 In the proton exchanger for a fuel cell according to claim 2, the basic compound is dissolved in a force forming some or all of the constituents of the ionic liquid or dissolved in the ionic liquid.

 Therefore, due to the low melting point and good proton conductivity of the ionic liquid, high proton conductivity is exhibited irrespective of the presence of water, and water generated in the power source of the fuel cell is not affected. It is possible to provide a proton exchanger that is insoluble.

 The proton exchanger for a fuel cell according to claim 3 contains a hydrophobic ionic liquid.

 Therefore, the proton exchanger using the above-mentioned hydrophobic ionic liquid has an effect that elution of ion'1 "raw liquid into water generated by the power source of the fuel cell can be suppressed.

 In the proton exchanger for a fuel cell according to claim 4, the ionic liquid and the polymer matrix form phenol.

 In the proton exchanger for a fuel cell according to claim 5, the polymer matrix formed as a gel with the ionic liquid has an ion exchange ability.

 Therefore, there is an effect that the proton conductivity of the proton exchanger can be further improved by the ion exchange ability of the polymer matrix.

In the proton exchanger for a fuel cell according to claim 6, the content of the polymer matrix in the gel comprising the ionic liquid and the polymer matrix is 3 to 20% by weight. It is in the range / ₀ .

Therefore, there is an effect that a proton exchanger capable of forming a membrane can be obtained with a much lower polymer content than a commonly used proton exchange membrane. Fuel cell proton exchange body according to claim 7, in order to suppress Kurosuo par of hydrogen in fuel cells, the hydrogen gas permeability 2x10- ⁴ cm ³ cm- - ¹ or less. Therefore, in the fuel cell using this proton exchanger, the effect of small polarization and high output is achieved.

Fuel cell proton exchanger of claim 8, in the normal temperature and non-humidified state, has a proton conductivity greater than 2x10 one ⁴ S cm.

 Therefore, the fuel cell using this exhibits high proton conductivity irrespective of the presence of water, and the components of the proton exchanger do not dissolve in the water generated in the battery power source. , Has an effect.

The proton exchanger for a fuel cell according to claim 9 exhibits a proton conductivity of 1 × 10 ¹² S cm or more under a non-humidified state at 100 ° C. or higher.

 Therefore, the water generated in the fuel cell power source gas is dissipated by gas, and furthermore, the proton exchanger exhibits high proton conductivity without depending on the presence of water, and furthermore, constitutes a proton exchanger. Since the salt is thermally stable, it is possible to provide a stable and high-performance fuel cell.

 The constituent element of the proton exchanger for a fuel cell according to claim 10 is water-insoluble. Therefore, in the fuel cell using this proton exchanger, the components of the ion exchanger cannot be eluted with respect to the water generated by the power source. This has the effect of greatly extending the life of the fuel cell.

 The proton exchanger for a fuel cell according to claim 11, wherein the constituent material is a thermally stable salt of a basic compound containing a hetero atom and an acid containing a fluorine atom and a sulfur atom in a molecule. And the molar ratio is in the range of 0.9 to 1.1 moles per mole of the former.

 Therefore, the fuel cell using the proton exchanger has an effect that a stable high-performance fuel cell can be provided even at a high temperature because the salt constituting the proton exchanger is thermally stable.

 A fuel cell according to claim 12 is configured to include the fuel cell proton exchanger according to any one of claims 1 to 11.

 Therefore, the fuel cell of the present invention, based on the above-described excellent properties of the proton exchanger, does not depend on water, does not elute components to water, and exhibits high performance over a long period of time at a high temperature. .

Claims

The scope of the claims  1. A proton exchanger for a fuel cell, comprising a basic compound containing at least one hetero atom.  2. The proton exchanger for a fuel cell according to claim 1, wherein the basic compound is dissolved in a force or an ionic liquid that forms part or all of the components of the ionic liquid. 3. The proton exchanger for a fuel cell according to claim 1, wherein the proton exchanger contains a hydrophobic ionic liquid.  4. The proton exchanger for a fuel cell according to any one of claims 1 to 3, wherein the proton exchanger forms a gel between the ionic liquid and the polymer matrix.  5. The proton exchanger for a fuel cell according to claim 4, wherein the proton exchanger has ion exchange capacity.  6. The proton exchanger for a fuel cell according to claim 4, wherein the content of the polymer matrix in the gel is in the range of 3 to 20% by weight, and the gel has a self-holding property. 7. Hydrogen gas permeability of the proton exchange ^{body, 2X10- 4 cm 3 cm- 1 s-} 1 or less請Motomeko 1 for fuel cell proton exchange body according to any one of 6. 8. Proton exchangers, cold and in non-humidified state, 2X10- ⁴ for fuel cell proton exchange recombinants according to any one of claims 1 to 7 having an S cm or more flop port tons conductivity. ■ 9. Pro tons exchangers, in non-humidified conditions for more than 100 ° C, 1X10- ² fuel cell protons exchanger according to any one of claims 1 to 8 having a S / cm or more proton conductivity .  10. The proton exchanger for a fuel cell according to any one of claims 1 to 9, wherein the constituent components of the proton exchanger are water-insoluble.  11. The components of the proton exchanger are salts of a basic compound containing at least one hetero atom and an acid containing a fluorine atom and a sulfur atom in the molecule, and the molar ratio of the basic compound is a basic compound. The proton exchanger for a fuel cell according to any one of claims 1 to 10, wherein the acid is in the range of 0.9 to L.1 on the basis of:  12. A fuel cell comprising the proton exchanger for a fuel funnel according to any one of claims 1 to 11.